Method and apparatus for continuous blending of granular materials

ABSTRACT

This invention relates to a method and apparatus for continuous blending of granular materials having the same or different particle size or density, comprising one or more containers tapered downwardly and inwardly, each having a stirrer rotatable about a vertical axis for stirring the granular material at the same time air is passed therethrough. Two or more stages in series may be arranged, either side-by-side or vertically in tandem, between which stages solids may be conveyed pneumatically or by gravity flow.

i United States Patent Max Leva 1030 Dallet Road, Pittsburgh, Pa. 15227825,570

May 19, I969 July 13, 197 I Inventor Appl. No. Filed Patented METHOD ANDAPPARATUS FOR CONTINUOUS BLENDING OF GRANULAR MATERIALS 9 Claims, 7Drawing Figs.

u.s.c|. 259/67, 259/1 l l Int.Cl. B0li 7/18 Field 0! Search 259/ 7, 8,67, 68, 66, 4, 95, 60, 64, 65

References Cited UNITED STATES PATENTS 2,685,499 8/1954 Hood 259/72,871,575 2/1959 DuPont 2,893,846 7/1959 Wistrich Primary ExaminerRobertW. Jenkins Attorney-William J. Ruano ABSTRACT: This invention relates toa method and apparatus for continuous blending of granular materialshaving the same or difierent particle size or density, comprising one ormore containers tapered downwardly and inwardly, each having a stirrerrotatable about a vertical axis for stirring the granular material atthe same time air is passed therethrough. Two or more stages in seriesmay be arranged, either side-byside or vertically in tandem, betweenwhich stages solids may be conveyed pneumatically or by gravity flow.

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PATENTEDJUUGIBYI 3,592,446

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his ATTORNEY METHOD AND APPARATUS FOR CGNTINUOUS ELENDING K GRANULARMATERIALS This invention relates to a method and apparatus forcontinuous blending of granular materials having the same or differentdensity or particle size and constitutes an improvement over thebatch-type method, such as described in my British Pat. No. 943,085.Since in the batch method, stirring must be i stopped and the containermust be emptied after each aerated blending operation, appreciable timeis consumed between the charging of one batch and that of the nextbatch.

Another disadvantage is that the capital investment per unit weight ofmaterial to be mixed is appreciable and the reproducibility of resultsis short of that desired.

Most blenders commonly used in the art operate on the principle oftumbling. However, homogeneous mixtures are not obtained when thedensity differences or particle sizes are appreciable. In such cases,tumbling effects actual separation of matter with the heavier layerparticles concentrating near the bottom of the bed.

An object of the present invention is to provide a novel method andapparatus for continuous aerated blending of granular materials so as toeffect substantial labor savings.

Another object is to provide a novel method and apparatus which involvessmaller capital investment and cost of operation than is obtainable bythe batch method.

A further object of the invention is to provide a novel method andapparatus for continuous blending of granular materials so as to obtainbetter overall reproducibility of blending results, in particular,better uniformity of the mixed materials.

A still further object of the invention is to provide an improvedapparatus having considerably greater capacity for a given floor space.

Another object of the invention as compared to the aforesaid tumblingprinciple and batch method is to render individual mixes more homogenousby keeping the heavier or larger particles in the charge in place, whileapplying careful mechanical stirring and just sufficient aeration sothat no segregation will result.

Other objects and advantages will become more apparent from a study ofthe following description taken with the accompanying drawings wherein:

FIG. I is an elevational view, partly in cross section, show ing asingle stage apparatus embodying the principles of my invention;

FIG. 2 is a schematic view of a two-stage machine embodying theinvention, wherein mixed particles of air are conveyed to the top of thesecond stage;

FIG. 3 is a two-stage machine wherein mixed particles and air from thefirst stage are pneumatically conducted to the bottom of the secondstage;

FIG. is a two-stage system, with the units arranged vertically intandem;

FIGS. 5 and 6 show a two-stage system in vertical tandem, as in FIG. 4but including certain modifications; and

FIG. 7 is a modification of FIG. 1.

Referring more particularly to FIG. 1 of the drawing, numetal 1 denotesa container substantially in the form ofa cone having a vertical shaftti which rotates on its axis and which supports, by frame (2a, aplurality of vanes or stirrers ob disposed around and along the entireheight of the shaft for thoroughly mixing the granular materials of thesame or difl'erent density or particle size fed therein through solidsinlet pipe 2. Low-pressure air is fed into air inlet pipe 4, passesthrough the entire height of the mixture and exhausts through outletpipe 5. The apparatus so far described is similar to that of thebatch-type apparatus disclosed in my British Pat. No. 943,085, exceptthe British apparatus has no solids inlet and outlet ports, whereas thepresent apparatus has both a solids inlet port as well as a solidsoutlet port. Also the outlet port of the present paratus isstrategically placed about onethird to one-fourth of the solids heightL. Moreover, synchronization of the solids inlet valve 2 and solidsoutlet valve 7 is provided which is an absolutely essential requirementfor continuous blending.

A screen or porous plate 8 is provided to prevent the solids fromentering pipe 4 at shutdowns. The solids are thus simultaneously stirredwhile air is passed therethrough and then exhausted through pipe 5,either into the atmosphere or into a O cyclone to recover any entrainedmatter. Container 1 may be completely emptied through discharge valve 7'and pipe 3' whenever desired, such as when new mixes are to be blended.

The essential feature of operation of the apparatus in FIG. I is thatthe rate of solids discharge through pipe 3 and valve 7 must besynchronized to the rate of introduction of the solids through inletpipe 2. Such synchronization may be achieved in various ways.Mechanically it may be accomplished by adjusting the opening ofdischarge valve 7 until the discharge rate is such as to keep the levelL at a constant height throughout the operation of continuous feeding ofsolids through inlet pipe 2. Perhaps the most likely method ofsynchronization is by way of determining the differential pressure AP ofair through the apparatus which is proportioned to L. Since thedifferential pressure is dependent upon the solids head which the airmust penetrate on its upward course, any variations in the level L ofthe solids will influence differential pressure.

However, the solids level L will vary only if the rate of feed is notthe same as the rate of discharge. Hence any level control apparatus,such as are well known in the art, may be used for actuating valve 2 inresponse to variations in level, L, so that the valve opening will bevaried to the extent necessary to keep the level L essentially constant.The most common type of mechanical apparatus for such level control maybe one similar to a float operated valve such as commonly used in waterclosets for toilets in that as the float on level L moves vertically itwill, by pivotal mechanical linkage, vary the opening of discharge valve7 or will merely effect opening or closing thereof sufficiently tomaintain the level L at a constant height. Still another method is tocause closing of selective contacts by a member, whose position iscontrolled by level L, so as to actuate a relay or motor which willoperate valve 2 to regulate it in accordance with variations in thelevel so as to keep the level substantially constant.

A typical control system is shown in FIG. 1. Electrodes D are verticallyadjustable so as to be set according to the desired AP. If the level Ldecreases below the desired level, an energizing circuit will becompleted through battery B and relay A so as to actuate and open inletvalve 2' to a greater extent and partially close valve 7 and thussynchronize the inlet and outlet flow of solids so as to maintain thedesired solids level or height L. If AP becomes too high, the flowthrough inlet valve 2' is reduced, and outlet valve 7 opens to a greaterextent. As a modification, either valve may be operated alone asdescribed.

FIG. 7 is a modification of FIG. I having a lower cylindrical sectionhaving a diameter d no more than one-half of the vessel diameter D andhaving a height L no more than onethird the height of L. L" is theheight from below the bottom of the cylindrical section.

FIG. 2 is a modification showing a typical two-stage machine wherein thematerials to be blended enter through inlet pipe 2 and low-pressure airenters the first stage through inlet pipe 4. The cleaning outlet 3' isalso connected to the pneumatic conveying line 3 for cleaning andemptying purposes. But the important operating solids transfer line isagain 3. The solids flow control valve 7 is synchronized with the inletflow through pipe 2 by any of the previously described methods. Themixed solids after stirring and simultaneous aeration are passedpneumatically through pipe 10 by virtue of the introduction oflow-pressure air at one end so as to pneumatically convey the partiallymixed solids into the top of the second stage by discharging the mixedsolids through baffle 11 so as to drop onto the top of the indicatedsolids level. Air is admitted through inlet pipe 4a into the bottom ofthe second stage and the solids control valve 7a is synchronized to thesolids feed rate to discharge the mixed solids through outlet pipe 9.Air is exhausted through the top outlet pipe a into the atmosphere or toa cyclone 24. That is, by selective operation of valves A and B, thecyclone 24 may or may not be used. For very fine particles, the cyclonemay be necessary.

FIG. 3 is a modified two-stage arrangement as in FIG. 2 except that thesolids after mixing in the first stage are not separately conveyed intothe top of the second stage by separate air but, instead, the solids arepneumatically con veyed directly into the bottom of the second stage bypipe Itlb into which air is fed at one end to provide not only formovement of the mixture in pipe 10b but at the same time fluidizing thecharge in the second stage in container lb at the right of FIG. 3.'Forbetter operation, the air entry tube 13 should be somewhat extended andcovered by a baffle 12 to prevent solids from falling back into the pipe101; at shutoffs. Instead of the baffle 12, a pipe with a bend at anangle ranging from 90 to 180 may be attached to the upper mouth portionof tube 13. As the conveying air carries the solids from stage no. I tostage no. 2, by entering the second stage the velocity of the airbecomes smaller and the conveyed solids deposit as a bed. For properoperation of such a system, the air velocity through pipe 10b must becarefully coordinated with that required to aerate the charge in thesecond stage. In some instances it may be necessary to provide secondaryaeration air either through 15 or 16.

The two stage system shown in either FIG. 2 or FIG. 3 is most suitablefor cases where carefully prepared blends are needed and where thesolids handled have sufiiciently good flow properties to permit transferpneumatically as shown. If desired, additional stages may be added toFIGS. 2 or 3 if more uniform blends are required.

As the solids are introduced into the second stage through pipe 10b, thebed is established in the second stage and stirred. As the level of thebed reaches the solids level indicated in FIG. 3, the mixed solids willoverflow and pass through adjustable valve 13 and outlet pipe I4.

FIG. 4 shows a two-stage machine but wherein the stages, instead ofbeing side by side as in FIGS. 2 and 3, are stacked or arrangedvertically in tandem. This arrangement has the advantage that only onestirrer motor and speed reducer is needed for both stages, because bothstirrers for stages I and 2 are on a common shaft. A sealing arrangementis provided for the stirrer shaft as it passes from the upper or firststage to the lower or second stage, thus eliminating the necessity forstuffing boxes and the like. To provide such seal, the solids bed itselfmay be used as will be explained hereinafter.

In operation, solids to be blended enter stage I through inlet pipe 2 toprovide a solids level L as shown. It should be noted that the solidswill be retained in the first stage, that is, in container 1, sincevalve 24 is closed and no appreciable amount of solids can fall throughthe bearing sleeve 21 which is inserted in the closing flange andthrough which the stirrer shaft 6-6c passes. Air is introduced throughvalve 17 while valve I8 remains closed and the charge is stirred. Assoon as sufficient stirring and simultaneous aeration occurs to providea homogenous mixture, valve 24 is opened so as to permit the nowpartially blended solids to overflow into the bottom container 10, thatis, the second stage. Before level L is obtained, air is admittedthrough inlet pipe 4c and through porous plate 80 and the stirrersalready in operation blend the solids to uniformity. As soon as thesolids level L is obtained, the solids control valve 7c is manipulatedand the mixed solids are discharged through outlet pipe 3c. The exhaustair from stage 2 may be passed either through valve 118 to assist withaeration of the first stage or it may be bypassed through pipe 19 to thetop of stage I and exhausted through pipe 3 to the atmosphere or toacyclone.

FIG. 5 shows a modification similar to FIG. 4 except that instead of aclosing flange 20 at the bottom portion 115d of the first stage, thereis provided an adjustable trough 22 formed externally of sleeve 23 andwhich may be vertically adjusted through a distance X for varying theopening and discharge rate from the first to the second stage.Low-pressure air is introduced into pipes I7d and 18d, each having avalve, also into pipe 4.

FIG. 6 shows in greater detail the adjustable valve of FIG. 5 comprisinga trough 25 formed around sleeve 26, which trough is verticallyadjustable by bolts 27 through a vertical distance x. By admitting air,either through valve 182 or l7e, the density of the solids column can becontrolled such that for a given clearance between cylindrical portionlSe and the bottom of trough 25, the solids will normally overflow fromstage I to stage 2 as illustrated in dotted lines. The solids in trough25 thus form a seal between stages.

Still simpler, the solids flow through the clearance x can be easiercontrolled by leaving either valve ll8e or I7e or both in an openposition and by regulating the vertical position of trough 25 by bolts27 or any other suitable mechanical means so that the rate of solidsflow through opening x is exactly equal to the feed rate in stage 1. Airis exhausted from the top of container Ie through air outlet tube 192into the atmosphere or a cyclone.

Of course, if desired, the blended solids discharged from the verticaltandem machine described in FIGS. 4, 5 and 6 may be fed from the bottomthereof to the top of an identical vertical tandem two-stage structureto provide a two- (or more) stage vertical tandem arrangement in series,similar to that described in FIG. 2 (or perhaps FIG. 3).

Thus it will be seen that l have provided a novel method and apparatusfor continuous blending of granular materials in one or two or morestages, either in series, side by side where the solids arepneumatically conveyed from stage to stage, or wherein the stages are invertical tandem and wherein the solids are simultaneously stirred andaerated and pneumatically conveyed after mixing from one stage to thenext; furthermore, l have provided a novel sealing arrangement forvertical tandem stages by way of a thick bed acting as a stuffing boxfor the stirrer.

While I have illustrated and described several modifications of myinvention, it will be understood that these are by way of illustrationonly and that various changes and modifications may be made within thecontemplation of my invention and within the scope of the followingclaims.

I claim:

I. A multistage continuous blending apparatus for granular materials,comprising a first container including stirring means and aerating meansfor simultaneously stirring and aerating granular materials introducedinto the top of the container, a second container also includingstirring means and aerating means for simultaneously stirring andaerating the contents thereof, and a discharge pipe adjacent the bottomof the first container and leading into the second container andconnected to a source of air so as to pneumatically conduct blendedsolids and air from the bottom of the first container through saiddischarge pipe to said second container.

2. A multistage apparatus as recited in claim I wherein said dischargepipe for pneumatically conveying blended particles is connected to thetop of said second container and wherein an air inlet valve introduceslow-pressure air into the bottom of said second container and wherein anoutlet valve discharges air from the top of said second container.

3. A multistage apparatus as recited in claim 1 wherein said dischargepipe for conducting blended particles from the first container isconnected to the bottom of said second container, and means in saidsecond container for preventing accumulation of granular material in theoutlet of said pipe.

4. Apparatus as recited in claim 3 together with a discharge pipe andcontrol valve therein disposed at the upper portion of said secondcontainer for regulating the level of mixed granular materials therein.

5. Apparatus as recited in claim I wherein said first and secondcontainers are arranged vertically in tandem with a common stirrershaft.

6. Apparatus as recited in claim 5 wherein a seal is provided at thebottom and'discharge end of the top container, said seal formed ofdischarged granular material and held in place by a closure flange whichsurrounds the common shaft of said stirrer. Y

7. Apparatus as recited in claim 5 wherein the discharge outlet of thetop container is in the form of a cylindrical portion of a downwardlytapered portion of the bottom of the container, a vertically adjustabletrough surrounding the common stirring shaft for said containers, andmeans for adjustably spacing said trough from the bottom edge of saidcylindrical portion so as to regulate the rate of discharge of blendedparticles discharged from the top container into the bottom container.

8. Apparatus as recited in claim 7 together with a bypass pipe leadingfrom an intermediate portion of the top container to the top portion ofthe bottom container, and a regulating valve in said bypass pipe.

9. Apparatus as recited in claim 7 together with a pair of air inletpipes, one connected to the bottom of the top container and the other,to the top of the bottom container, and a second bypass pipe connectingthe top portions of said bottom and top containers and including aregulating valve therein.

1. A multistage continuous blending apparatus for granular materials,comprising a first container including stirring means and aerating meansfor simultaneously stirring and aerating granular materials introducedinto the top of the container, a second container also includingstirring means and aerating means for simultaneously stirring andaerating the contents thereof, and a discharge pipe adjacent the bottomof the first container and leading into the second container andconnected to a source of air so as to pneumatically conduct blendedsolids and air from the bottom of the first container through saiddischarge pipe to said second container.
 2. A multistage apparatus asrecited in claim 1 wherein said discharge pipe for pneumaticallyconveying blended particles is connected to the top of said secondcontainer and wherein an air inlet valve introduces low-pressure airinto the bottom of said second container and wherein an outlet valvedischarges air from the top of said second container.
 3. A multistageapparatus as recited in claim 1 wherein said discharge pipe forconducting blended particles from the first container is connected tothe bottom of said second container, and means in said second containerfor preventing accumulation of granular material in the outlet of saidpipe.
 4. Apparatus as recited in claim 3 together with a discharge pipeand control valve therein disposed at the upper portion of said secondcontainer for regulating the level of mixed granular materials therein.5. Apparatus as recited in claim 1 wherein said first and secondcontainers are arranged vertically in tandem with a common stirrershaft.
 6. Apparatus as recited in claim 5 wherein a seal is provided atthe bottom and discharge end of the top container, said seal formed ofdischarged granular material and held in place by a closure flange whichsurrounds the common shaft of said stirrer.
 7. Apparatus as recited inclaim 5 wherein the discharge outlet of the top container is in the formof a cylindrical portion of a downwardly tapered portion of the bottomof the container, a vertically adjustable trough surrounding the commonstirring shaft for said containers, and means for adjustably spacingsaid trough from the bottom edge of said cylindrical portion so as toregulate the rate of discharge of blended particles discharged from thetop container into the bottom container.
 8. Apparatus as recited inclaim 7 together with a bypass pipe leading from an intermediate portionof the top container to the top portion of the bottom container, and aregulating valve in said bypass pipe.
 9. Apparatus as recited in claim 7together with a pair of air inlet pipes, one connected to the bottom ofthe top container and the other, to the top of the bottom container, anda second bypass pipe connecting the top portions of said bottom and topcontainers and including a regulating valve therein.